1. Field of the Invention
This invention relates to a valve and more particularly to a rotary valve having a valve stem sealed by a bellows with the stem end portions displaced in parallel relationship and rotatably connected to an actuator having an axis aligned with the lower axis of the valve stem and offset from the upper axis of the valve stem so that rotation is transmitted from the actuator to the valve stem through a pressure boundary formed by the bellows.
2. Description of the Prior Art
In rotary valves, such as butterfly, ball, plug and the like for conveyance of fluids and particularly contaminated fluids at high pressure, as well as, at substantially reduced pressure or under vacuum conditions, it is preferred to utilize static seals as opposed to packed or dynamic seals. Packed or dynamic seals are subject to wear and this results in valve leakage, particularly at the pressure boundary between the valve stem and the valve member. A commonly used static seal is a bellows surrounding the valve stem. U.S. Pat. Nos. 1,644,825; 2,659,569; 2,659,570 and 3,811,651 disclose valves that utilize a bellows for sealing around the valve stem between the valve actuator and the valve member.
Conventionally, a bellows, when used to seal a valve stem, is bonded or welded to the structure of the valve body that supports the rotatable valve member at one end and at the opposite end to a retainer or cap that connects the valve stem to the valve actuator. This arrangement is illustrated in U.S. Pat. No. 3,811,651. Because the connections at the ends of the bellows are stationary, a static seal is formed. It is known to laterally deflect the valve stem or utilize a crank-like valve stem and hermetically seal the stem in the bellows. In this manner, the valve stem connects the actuator to the valve member to produce rotational movement of the valve member, as illustrated in U.S. Pat. Nos. 1,644,825 and 3,811,651.
One of the difficulties encountered with a bent valve stems hermetically sealed in a bellows and operated by a crank-like actuator is binding of the rotatable end of the valve stem positioned in the retainer or cap within the valve actuator. Particularly in high pressure applications, the line pressure exerts an upward force upon the valve stem and the bellows cap tending to laterally displace the valve stem and the bellows cap. If the upper end of the valve stem and/or bellows cap becomes laterally displaced with respect to the axis of rotation of the actuator, frictional contact between the valve stem, bellows cap and the retainer occurs and inhibits relative rotation between the actuator and the valve stem. As a result, rotation of the actuator will not produce rotation of the valve stem or rotation will be obstructed to such an extent that the valve cannot be positively opened or closed.
While it has been suggested by the prior art devices to use a bellows to hermetically seal a valve stem, the use of a bellows has only been applicable as a static seal or an axially movable seal and not as a rotary seal where the bellows is subjected to torsional loading. Therefore, there is a need in rotary valves for a rotary seal of a valve stem by a bellows that is connected to an actuator in a manner to permit tranmission of torque through the bellows to the valve stem while maintaining a pressure boundary around the valve stem.